Biochar is a carbon-rich product obtained when biomass is heated in a closed container with little or no available air. It is usually used to improve soil fertility and sequester carbon in an effort to mitigate climate change. Biochar has been made and used in soils for hundreds of years by cultures in the Amazon region, but research on biochar and its effects is still ongoing. This article aims to provide an overview of current biochar research based on available peer-reviewed papers and studies.
Biochar has multiple proposed benefits for soil and the environment. It has been found to increase soil fertility by enhancing soil nutrients and water retention capacity. Biochar application to soil has been shown to increase crop yields in many field trials and studies. The porous structure and large surface area of biochar provides habitat and nutrients for soil microbes. This promotes decomposition of organic matter and release of plant-available nutrients. Additionally, biochar application has been demonstrated to reduce nitrous oxide emissions and leaching of nitrate and phosphate from soils into groundwater.
One of the major incentives for research into biochar is its potential as a carbon sequestration strategy. Biochar is highly stable and resistant to degradation in soils. Estimates in scientific studies suggest that about 50% of the carbon in biomass can be sequestered in biochar for hundreds to thousands of years when applied to and retained within soils. Various factors such as feedstock type, production conditions, and soil properties determine the degree of carbon stabilization achieved by biochar amendment. Tropical soils tend to stabilize biochar carbon for longer durations compared to temperate or boreal soils.
Many research studies have been conducted to understand how feedstock and production conditions influence the physical, chemical, and biological properties of biochar that determine its impacts on soil and agricultural systems. Different feedstocks such as wood, corn stover, rice husks, and animal manures will produce biochars with varying elemental compositions, surface area, and pore structure depending on pyrolysis temperatures and heating rates. Higher pyrolysis temperatures generally result in higher carbon content and aromaticity but lower nutrient contents in biochar. Slower heating rates allow volatiles to escape and produce highly porous biochar structures ideal for water and nutrient retention in soil.
Several meta-analyses have synthesized data from biochar field trials and greenhouse pot experiments. Ippolito et al. reviewed 74 studies and found that biochar application increased crop yields in 55% of cases, with increases of 10% on average. Major yield increases tended to occur on degraded or nutrient-poor soils. Jeffery et al. analyzed biochar field experiments across four continents and reported median crop yield increases of 10% for all crops and locations. Results from pot and field experiments have demonstrated that biochar effects on crop growth are most significant in the first 1-2 years after application, before leveling off or decreasing gradually as the biochar ages within soils.
Researchers are developing new technologies to integrate biochar production with existing waste and residues from agricultural, forestry and municipal sectors. Pyrolysis systems can be modified to co-produce bio-oil and synthesis gas along with biochar. The bio-oil and gas fractions have higher energetic values than raw biomass and can be utilized for heat, power and transport fuel applications. At the same time, the biochar solid byproduct provides an outlet for recycling nutrients and carbon back to lands. Life cycle assessment studies indicate that such integrated biorefinery approaches to biochar production have lower greenhouse gas footprints than traditional waste management practices like open burning or dumping in landfills.
Overall, scientific evidence increasingly confirms the technical feasibility and multiple environmental benefits of biochar. Economically viable scaling and long-term impacts on ecology and ecosystem services require more research. Areas that need further investigation include biochar effects on soil biological communities, trace gas emissions over decades, leaching risks from different production systems, standards and certification processes. Optimization of feedstocks and pyrolysis conditions also remains critical to maximize carbon sequestration potentials. Continued scientific advancement will guide sustainable implementation of biochar applications across landscapes and support paradigm shifts towards bio-based green economies.
This article has provided an overview of current research on biochar based on examination of peer-reviewed scientific studies and field trials in published papers. Findings indicate that biochar can enhance soil fertility, increase crop yields, reduce emissions and leachate losses from fertilized lands when applied judiciously. Biochar also represents a viable strategy for long-term carbon sequestration from biomass. Additional research is still needed to fully understand ecological impacts, optimize production methods and enable large-scale adoption of biochar systems for societal benefits.